Specify date math with URI encoding in rollover API docs

Closes #21181

docs/reference/indices/rollover-index.asciidoc

@@ -95,7 +95,8 @@ over. For instance:
 
 [source,js]
 --------------------------------------------------
-PUT /<logs-{now/d}-1> <1>
+# PUT /<logs-{now/d}-1> with URI encoding:
+PUT /%3Clogs-%7Bnow%2Fd%7D-1%3E <1>
 {
   "aliases": {
     "logs_write": {}